Technologies and Applications

FemtoSci Technologies and Applications

This section illustrates the wide variety of novel technologies and applications for enhancing the electrical and mechanical properties of complex electronic, fluid or mechanical systems through the utilization of unique material and material combinations, primarily related to diamond, nanodiamond or diamond-like-carbon, often  for devices in combination with silicon and other well-known semiconductor processing and packaging technologies. Enhancement of fluid and mechanical systems is generally accomplished through special processing of nanodiamond for dis-aggregation and functionalization. 

In the area of electronic systems, diamond can be utilized as single crystal material, or within the last several years, FemtoSci, has developed processing techniques for CVD (chemical vapor deposition) that achieves design control over grain-size and purity. This enables poly-diamond films to be deposited with grain sizes with sizes equivalent to or greater than film thickness; these films behave in most respects as single-crystal diamond, at a small fraction of the manufacturing cost. These films can be utilized in passive electronic components, high power resistors, capacitors, active devices (electronic control valves – transistors), and sensors and detectors for a wide range of physical parameters (e.g. radiation, temperature, gas concentration, etc.)

Diamond is a unique material, being the hardest material known, and a wide band-gap (5.5 eV), It serves as a mechanically indestructible agent (resilient to displacement damage by radiation or direct mechanical stress), an extremely effective electrical insulator, and yet as a semiconductor it can be doped to achieve electrical conduction and control with extremely low leakage.

FemtoSciI leadership personnel (see Services and Leadership) have served as principle investigators (PIs),  Co-PIs, or Project Leaders in a wide range of applications over a cumulative experience of over more than 60 years and contributed and managed a cumulative budget well over $100M.  Much of this work was performed at Vanderbilt University ( by a FemtoSci principal; see related figures), often under contract or grant support by agencies or companies noted where appropriate . FemtoSci's wide-ranging experience provides a unique capability to solve challenging electronic, thermal and mechanical solutions to engineering problems arising in extreme environments. FemtoSci embraces the fab-less approach for creating leading edge technologies with maximum flexibility. Many critical fabrication processes are subcontracted to reliable and pre-certified facilities such as Vanderbilt University, Auburn University, University of Louisville, and other reputable and established commercial facilities with which FemtoSci has standing arrangements or prior experience for fabrication and analysis. 

NanoDiamond-Based Additives for Composites and Liquids to Achieve Enhanced Performance

FemtoSci works with functionalized nanodiamond particles to enhance the thermal, mechanical, and electrical properties of liquid and solid materials for applications in transformer cooling, thermal management of power electronics and other heat-generating processes and systems.

Functionalized Nanodiamond for Increased Performance of Transformer Oil

FemtoSci has produced and evaluated functionalized nanodiamond additives to various oils appropriate for power transformer cooling. The plot shown indicates a greater than 25% improvement in oil thermal conductivity at less than 100 PPM nanodiamond additive. 

The data here shows a thermosetting resin with processed nanodiamond additive which results in a composite that is significantly stiffer and stronger without a sacrifice in ductility. Testing has shown that this improves the flexural modulus and strength of vinyl ester resins by almost 50-percent with no loss in ductility. The blue bar is the reference with no nanodiamond; the red bar is 0.6% nanodiamond and the green bar is 1.2% nanodiamond.

Thermal conductivity is also increased with the functionalized nanodiamond additive at levels greater than fractions of a percent.

The nanodiamond additive consists of particle so small, that they randomize in the plastic melt, and do not contribute to any abrasion or erosion of plastic (injection) molds.  If fact, lubricity of the melt is increased and mold life is not compromised, but extended. 

Ultra-Capacitors for Extreme Environments - Extreme Capacitance per Volume - Negligible Change in Capacitance over Temperature

The figures illustrate the application of FemtoSci technology to create advanced high voltage (> 80 kV), high energy density (> 2 J/cm3) capacitors utilizing chemical vapor deposition (CVD) diamond in conjunction with a robust electrode metallurgy and packaging approach. These capacitors will achieve a temperature coefficient of capacitance of 10 ppm/°C, and are capable of rapid charging and discharging (< 400 ns) over thousands of cycles.

The recent advent of high quality CVD diamond (as opposed to natural or High Pressure, High Temperature [HPHT] formation) has opened the door for its practical development into a useful capacitor technology. Among the factors that make diamond the ideal dielectric material for advanced capacitors are its highest dielectric breakdown strength (30 MV/cm) and highest thermal conductivity (2000 W/mK) of known materials. FemtoSci is uniquely positioned and qualified to develop, qualify, and transition to volume manufacture this technology in partnership with its partner company, APEI,  with expert packaging and high voltage experience, while providing multiple pathways for commercialization and cost reduction.

The technology to deposit layers of diamond and fabricate a diamond dielectric capacitor has been demonstrated.   In a prior program executed by members of the FemtoSci team a diamond test capacitor was created.  The prototype capacitor design was based on a two inch silicon substrate with a 20 micron thick diamond coating.  The thickness was chosen based on a previously measured breakdown strength of 3,000 volts/micron or 30 Megavolts per cm and a design criteria of 60,000 volts ultimate breakdown.  With an operational voltage of 40,000 volts, the 50% over-voltage design provides a high reliability capacitor.

Passive Resistors Compatible with Extreme Environments

Sensors / Detectors in Extreme Environments:

Diamond-Based Gas Sensors

The steady state and  transient response of a diamond-based gas sensor is shown, with fast repeatable gas monitoring at 300 DEGREES C.

These nanodiamond hydrogen sensors were deployed on the launch pad of the USA Shuttle missions by NASA to detect leakage of hydrogen gas before launch. 

Diamond Based Accelerometers and Pressure Sensors

The moving anode approach to the diamond-based accelerometer is a very novel way to relate g-forces to signal current change with the diamond emitter.  Electron emission in the cathode-anode emitter device is governed by cold cathode behavior, which is to say it obeys the Fowler-Nordheim equation for Fowler-Nordheim tunneling. As the moving anode moves under the effect of an external G force, the FE current from each cathode varies significantly, and is related to sensed acceleration.

This is a simplified view of an accelerometer. Acceleration in the direction perpendicular to the chip causes a difference in the spacing of the cathode and the anode;  the Fowler-Norheim emission current is strongly depend on electric field; as the proof mass (PM) moves, the field changes, and the cathode current is extremely sensitive to this change, and provides an electrical current response to sensed acceleration.

Diamond-Based Pressure sensors are unique in their ability to function a temperatures above 500 degrees Centigrade, and maintain accurate functionality.

Diamond Radiation Detectors - Example of Neutron Detector

While high energy neutrons can be detected by reactions directly with the carbon in diamond, it is generally true that thermal neutron sensing is critical. In reactor monitoring, for examplel, a significant fraction of extra-core neutrons are thermal.

The most common materials used for converting an incoming thermal neutron to a charged particle, which are also compatible with solid-state detector fabrication, are the Boron-10 and the Lithium-6 reaction. The boron reaction is given as:                                                   B10 + n     >>>>>>       Li7+  α

The alpha particle, in the above equation, has an energy of 1.47 MeV.  The boron reaction has a cross section of 3840 barns to thermal neutrons, which is a respectable cross section. By comparison, the “gold standard”, helium 3 reaction has a cross section of 5330 barns. Another consideration for this reaction is that the B10 isotope occurs 19.8% in natural boron, making the use of concentrated B10 unnecessary in high flux sensing, which provides an additional cost advantage. It is important to note, that the concentrated isotope is readily available.  FemtoSci has run Stopping and Range of Ions in Matter (SRIM) simulations to determine the range of a 1.47 MeV alpha particle in diamond. The simulations yielded the range of the alpha particle in diamond to be approximately 3 microns. Therefore, for maximum collection benefit, the detector structures must take into consideration that the total charge deposited will occur within a limited distance of the conversion layer.

The following figure shows one time "snap shot" of an alpha particle (generated in the conversion layer from a neutron strike)) entering the detecting device. The hole and electron pairs generated are swept to opposite sides (top and bottom) due to the applied field, resulting in a current pulse which is measurable, and records the detection of a neutron strike. 

The following figure show the typical structure of a diamond-based neutron detector developed by FemtoSci. 

Active Devices - Diodes and Triodes

Active devices such as diodes and triodes (which can actively control the flow of current) have been fabricated using diamond-based technology. These devices operate with essentially no change in behavior above 500 degrees C, and because electron flow does not go through a semiconductor.....rather through a vacuum or intrinsic diamond, these devices are essentially radiation immune, both to total dose, and gamma dot (transient pulse radiation.)